CHAPTER XXIX. 



PTERIDOSPERMEAE. 



I. LYGINOPTERIDEAE. 

 LYGINOPTERIS. 



The genus Lyginopteris is selected for tlie first place in this 

 chapter simply on the ground that we have a fuller knowledge of 

 its morphology than in the case of other types. It is not regarded 

 as the most primitive member of its class. Lyginopteris may be 

 described in a few words as a plant having the habit and to a large 

 extent the anatomical features of a Fern, but differing from existing 

 ferns in the possession of integumented megasporangia or seeds 

 and in the power of secondary growth in thickness by means of 

 a cambium in both stem and root. The seed (Lagenostoma) 

 agrees with those of recent Cycads and Gnetales more closely 

 than with the corresponding organs in Conifers or any other group, 

 while the structure of the secondary wood is practically identical 

 with that of Cycads. The microsporangia occur as groups of 

 small bilocular sporangia, or synangia, at the tips of fertile pinnae 

 of highly compound fronds. 



Nomenclature and Historical Summary. In 1866 B. W. Binney'- 

 of Manchester published a short description of a small petrified 

 stem from the Lower Coal Measures of Lancashire and named it 

 Dadoxylon oldhamium, employing Endhcher's term Dadoxylon 

 which that author substituted for Pinites as previously used by 

 Witham^- Three years later Williamson* drew attention to 

 certain features in which Binney's type differs from the genus 

 Dadoxylon and substituted a new name Dictyoxylon, suggested 

 by the reticulate pitting on the walls of the tracheids. In a 

 1 Binuey (66). " Unger (50) A. p. 378. ' Waiiamsou (69). 



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